Quote:
Originally Posted by YamahaFreak
I have new measurements, now that my meter is properly set to DC voltage. On startup, VS voltage briefly peaks at 211 VDC, then drops, at first sharply and then slower and slower until finally settling at 11 VDC after about a minute. VA voltage peaks at 57 VDC at startup, then quickly falls off to zero.
See the attached image for the power supply board part numbers - there are several BN44 numbers.
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Those sound about right. Check the panel, there's a sticker that will give you those voltages.
If the 212 is high (I think it's OK), then the power supply will shut itself down. There's generally a VS adjustment on the power supply. You can try moving it a few degrees counter clockwise and see if the voltage matches the label. If it's high, I've found a small value electrolytic up in that area that goes high ESR.
If the voltages are correct, I think you may have a problem at a buffer (cue scary music) that's shutting down the sustain, which tells the control board, which shuts down the power supply.
Before you do, go over the entire surface of the screen with a bright flashlight and look for a teensy tiny bullet type star crack anywhere on the screen. If it has one, it won't be on the outer surface but on the face of the pixels (internal glass). If you find one, or a burned pixel, stop there. The panel is bad and the game is over. If you don't see any cracks or burned pixels, then let's check the scan buffers.
I have a shortcut I came up with to quickly test the scan buffers, but it requires a DMM with a diode scale. I've always used a Fluke for this test but yours should work fine if it has a diode scale.
Flip open any one of the ribbon connectors that connect to the display, and put the negative probe of your meter on *any* of the connections at the connector. The pin spacing is tiny and your meter probe will probably cover at least two, but that's not a problem as we're going to do a batch test of all the output lines of the scan buffer chips on the buffer boards.
So with the meter on diode, and the negative lead on any pin under the ribbon connector, put your positive lead on any of the edge connectors between the scan buffers and the sustain. Move the probe until you get a diode reading (0.6V give or take a tenth). Once you found the right spot, slide the positive probe across all the pins for each of the ribbon connectors. Do this slowly and keep an eye on the meter. If the indicated voltage on the meter drops to zero, there's a shorted scan line on the output side of the buffer. A single scan line will shut the whole shooting match (East Coast expression) down. My experience is that when I find one bad scan line, there's close to a dozen more. All of them coming from the same buffer IC.
If you find that as you move to another connector the meter voltage goes high, move your negative lead until you once again are reading a junction in circuit (0.6v).
If all lines test clear, then you may have a bad Y main (sustain), X main, control board, or main.
John